Printing Ink Wastewater Research Articles

Validity of zinc oxide nanoparticles biosynthesized in food wastes extract in treating real samples of printing ink wastewater; prediction models using feed-forward neural network (FFNN)

In the present study, biosynthesized ZnO nanoparticles in food wastewater extract (FWEZnO NPs) was used in the photocatalytic degradation of real samples of printing ink wastewater. FWEZnO NPs were prepared using green synthesis methods using a composite food waste sample (2 kg) consisted of rice 30%, bread 20 %, fruits 10 %, chicken 10 %, lamb 10%, and vegetable 20%. The photocatalysis process was optimized using response surface methodology (RSM) as a function of time (15–180 min), pH 2–10 and FWEZnO NP (20–120 mg/100 mL), while the print ink effluent after each treatment process was evaluated using UV–Vis-spectrophotometer. The behaviour of printing ink wastewater samples for photocatalytic degradation and responses for independent factors were simulated using feed-forward neural network (FFNN). FWEZnO NPs having 62.48 % of the purity with size between 18 and 25 nm semicrystalline nature. The main functional groups were –CH, CH2, and –OH, while lipid, carbon-hydrogen stretching, and amino acids were the main component in FWEZnO NP, which contributed to the adsorption of ink in the initial stage of photocatalysis. The optimal conditions for printing ink wastewater were recorded after 17 min, at pH 9 and with 20 mg/100 mL of FWEZnO NPs, at which the decolorization was 85.62 vs. 82.13% of the predicted and actual results, respectively, with R2 of 0.7777. The most significant factor in the photocatalytic degradation was time and FWEZnO NPs. The FFNN models revealed that FWEZnO NPs exhibit consistency in the next generation of data (large-scale application) with an low errors (R2 0.8693 with accuracy of 82.89%). The findings showing a small amount of catalyst is needed for effective breakdown of dyes in real samples of printing ink wastewater.

Removal of Congo red dye from industrial effluents using metal oxide-clay nanocomposites: Insight into adsorption and precipitation mechanisms

The efficacy of magnesium oxide (MgO)-bentonite clay nanocomposite particles (MgO nanoparticles embedded in powdered bentonite clay) for water and wastewater treatment applications is examined herein. Congo red (CR), a widely used azo dye, was used as the model contaminant. For CR concentrations ≤120 mg/L, the optimum nanocomposite dosage was ≤1 g/L, achieving CR removal ≥99% for contact times (mixing durations) ≤10 min, whereas temperature and pH had no significant effect on the treatment process. The removal of CR dye followed the pseudo-second-order model than the first order model. Furthermore, adsorption isotherms followed the Langmuir adsorption isotherm rather than the Freundlich adsorption isotherm (R2 ≥ 0.99), hence confirming monolayer homogenous adsorption. The surface morphological and physicochemical characteristics of the nanocomposite were also identified, and results suggest that CR removal was governed by electrostatic attraction between the protonated hydroxyl groups (i.e., -OH2+), embedded on the nanocomposite surface, and the negatively charged –SO3-groups of the CR dye. When used for the treatment of real printing ink wastewater, CR was practically removed (⁓100%), whereas for real printing and dyeing wastewater (PDW), a more challenging effluent that also contains salts and other contaminants, CR removal was ≥80%. Overall, the produced MgO-bentonite clay nanocomposite hold great promise for sustainable CR removal, a typical contaminant that is released by many industries including printing, tannery and textile, paper, plastic, and paint and coatings.

Printing ink wastewater treatment using combined hydrodynamic cavitation and pH fixation.

Printing ink wastewater (PIW) carries a heavy load of pollutants, the composition of which makes treatment difficult, especially when trying to minimize the pollution load. According to the latter, the present study aims to investigate PIW treatment with different various methods and to determine the maximum color, COD (chemical oxygen demand) and TSS (total suspended solids) removal. First, hydrodynamic cavitation (HC) was tested and the effect of hydrogen peroxide dosage (0-10gL-1), and pH (3, 5, 8, 10) was examined concerning the removal of PIW initial COD concentrations 4000 and 8000mgL-1. Removal was high (more than 81%) only at pH 5 in HC reactor. The second method involved treatment with separate pH fixation of the undiluted PIW (COD 17000mgL-1, actual pH 8±0.2). This treatment, maximized removals, reaching reduction of the initial values more than 91%, at pH 5. Finally, PIW was treated with a combination of the above methods, leading to 93-97% removals for 8000mgL-1 PIW treatment and 97-99% for 17000mgL-1 PIW respectively. Process cost calculations showed that the latter method is an effective and affordable treatment method for PIW streams, while toxicity tests of the treated PIW showed substantial toxicity reduction.

Printing Ink Wastewater Treatment Using Hydrodynamic Cavitation and Coagulants/Flocculants

Raw printing ink wastewater (PIW) was treated with various inorganic coagulants and organic flocculants (anionic and cationic polyacrylamides). These processes were also examined as post treatment step following hydrodynamic cavitation. Treatment effectiveness was assessed through color, chemical oxygen demand (COD) and total suspended solids (TSS) removal. The addition of 4500 mg L−1 polyaluminum chloride coagulant in undiluted PIW (COD: 17000 mg L−1) resulted in 99% color removal, 96% COD and TSS removal, after settling for 2 h. The addition of 10 mg L−1 of anionic polyacrylamides in the sample reduced settling time to only 5 min, with concomitant 96–98% removal efficiency. The addition of a 4 min hydrodynamic cavitation pretreatment step reduced coagulant addition by 33%, for the treatment of undiluted PIW (with 10 mg L−1 anionic polyacrylamide), while removals were ranged between 96 and 98%. Economic analysis for the undiluted PIW showed that costs were reduced by ca. 20% with the hydrodynamic cavitation pretreatment step. Moreover, sludge characterization showed the presence of maghemite, aluminum chloride and potassium aluminum silicate. Finally, toxicity tests revealed a significant attenuation of the toxic potential of undiluted PIW, thus indicating the enhanced efficiency of the proposed combined process (hydrodynamic cavitation and coagulation/flocculation).

Treatment of printing ink wastewater using a continuous flow electrocoagulation reactor

Printing ink wastewater from printing facilities is difficult to treat because of its heavy pollutant load (chemical oxygen demand - COD, color and total suspended solids - TSS). In this study undiluted printing ink wastewater with high COD (i.e., 20,000 mgL−1) was treated using a highly efficient, continuous flow electrocoagulation reactor with aluminum electrodes. The parameters investigated were: initial COD concentration (4000, 10,000 and 20,000 mgL−1), current density (21, 42 and 83 mAcm−2), and inlet flow rate (6, 8 and 10 mLmin-1). All parameters showed great efficiency in terms of pollutant removal for diluted printing ink wastewater. For undiluted printing ink wastewater treatment, COD, color, and TSS removal were maximized at 6 mLmin-1 flow rate reaching 82%, 98%, and 85% COD, color, and TSS removal, respectively, by applying the lower tested current density 21 mAcm−2. COD, color and TSS removal increased with increasing current density. For undiluted printing ink wastewater and a flow rate of 8 mLmin-1, COD removal was between 42 and 88%, color reduction between 85 and 99%, and TSS reduction between 83 and 98% when the applied current was increased (from 21 to 83 mAcm−2). Lower pollutant removal was observed at the highest flow rate of 10 mLmin-1 for all current densities tested. Process cost calculations in terms of electrical energy, electrode material consumption and sludge disposal, showed that the use of continuous flow electrocoagulation reactor (with flow rate 6 mLmin-1, and at 21 mAcm−2) is an affordable and effective treatment method for printing ink wastewater streams with very high COD. Sludge characterization showed Al-silicate-rich sludge. Particle sizes increased after treatment and Cu and Ti were detected in the sludge. A post-treatment stage is necessary before discharging effluent into water bodies.

Pilot-scale hybrid system combining hydrodynamic cavitation and sedimentation for the decolorization of industrial inks and printing ink wastewater

A pilot-scale hydrodynamic cavitation (HC) system followed by sedimentation (SED) was used for the decolorization of 5 industrial-grade inks, a fluid containing a mixture of the five industrial grade inks (MIX) and printing ink wastewater (PIW). The pilot scale HC reactor combines a Venturi tube with a 31 holes orifice plate accommodated in the vena-contracta of Venturi. The study aimed to define optimal operating conditions, i.e., hydrogen peroxide concentration (H2O2), pH and combined HC/SED treatment time, to achieve decolorization and reduce HC operation time. Under the optimal conditions at the proposed HC/SED system, color removal reached 92%, 91%, 90%,98% and 90%, for black, red, yellow, cyan, and green ink respectively (at pH 8 without H2O2 addition). In the same system, color removal for PIW was 92%, whereas for MIX decolorization reached more than 90% for all the wavelengths in the selected spectrum 300–700 nm at HC/SED system (at pH 8 and 1 g L-1 hydrogen peroxide). The suspended particles were characterized by measurements of the particle size distribution and of the respective zeta potential. The equivalent cavitation yields, electric energy consumption and operating costs were calculated. The present work's results suggested that HC combined with sedimentation has a great potential for real applications and is superior compared to other technologies (i.e., H2O2 alone, sedimentation alone or even HC with or without H2O).

Experimental investigation on the oxidation of printing ink wastewater under hydrothermal flames

Printing ink wastewater has a strong color and contains high salinity and high concentrations of complex organic compounds, posting a severe threat to the ecological environment and human health. In this work, supercritical water oxidation of printing ink wastewater is performed within a transpiring wall reactor (TWR) to avoid corrosion and salt plugging issues. The high concentration of organic matter in printing ink wastewater is used to form hydrothermal flames for enhanced degradation. Flame temperatures, gaseous and aqueous products characteristics, as well as the anti-corrosion and salt plugging performance of the reactor, are obtained. A remarkable temperature fluctuation due to the multi-component systems indicates the instability of hydrothermal flame. The salt recovery rate of 94.56% and the integrity of the porous tube inner wall indicate that TWR has a good performance in terms of anti-corrosion and salt plugging. Under typical conditions, the removal rates for chemical oxygen demand, total nitrogen, and color are 99.52%, 70.07%, and 97.89%, respectively. Alkanes, nitrogenous compounds, benzodiazepines, and heterocyclic compounds in the aqueous products, and CO, H2, NH3, and CH4 in the gaseous products are the main intermediate products of printing ink wastewater under hydrothermal flames. Ammonia nitrogen, as the main intermediate product, inhibits the complete oxidation of nitrogenous organic compounds. Additionally, higher KNO3 concentrations promote the complete oxidation of nitrogenous organic compounds, while higher NaOH concentrations can increase the pH value and slightly facilitate degradation. In addition, higher feed flow rates prevent deposition and adhesion of additives that occur at high concentrations.

Treatment of real industrial-grade dye solutions and printing ink wastewater using a novel pilot-scale hydrodynamic cavitation reactor

A novel pilot-scale hydrodynamic cavitation (HC) reactor was used to decolorize industrial-grade dye solutions and printing ink wastewater (PIW). The effect of the orifice plate geometry (1 hole plate of 1 mm and 2 mm in diameter, 31 holes of 1 mm and 2 mm in diameter, 62 holes of 1 mm and 2 mm in diameter), inlet pressure (4, 5 bar), initial dye concentration (0.3 and 0.6 OD), and the synergistic effect of HC and hydrogen peroxide concentration (0.0, 0.5, 1.0, 2.0 g/L) were investigated. The results showed that the highest color removal was obtained using 31 holes orifice plate of 2 mm holes’ diameter, at 4 bar inlet pressure. Furthermore, although HC could not degrade completely all the industrial-grade dyes, efficiency was enhanced in the presence of H2O2. The optimum concentration of hydrogen peroxide was 1.0 g/L regardless of the initial concentration of the dyes studied. Under optimum operating conditions, color removal reached up to 68% for black, 39% for red, 43% for yellow, 55% for green, and 51% for cyan dye, while color removal in the PIW reached only 15%. The black dye solution presented almost 100% COD removal, while 38%, 25%, 67%, and 78% COD removal values were obtained for the red, yellow, cyan and green dyes, respectively. 55% COD removal was recorded from the PIW. Concerning cavitation yields, black, red, yellow, green, cyan dye yields reached 2.5E(-7), 1.1E(-7), 1.5E(-7), 2.0E(-7), 1.7E(-7) OD⋅L/J, respectively, while PIW yield was 6.3E(-8) OD⋅L/J. The present study demonstrates that HC combined with green oxidants such as hydrogen peroxide could be an alternative treatment approach for real industrial wastewater streams. However, a combination with a post-treatment method should be applied to maximize both color and COD removal.

COD Treatment of Printing Ink Wastewater by Column Adsorption using Activated Carbon

Direct discharge of untreated industrial effluents containing high COD is hazardous to the environment. This study explores the efficiency of commercial activated carbon to uptake of the organic components responsible for the chemical oxygen demand of ink wastewater by column adsorption. The main objective of this research is to reduce the COD of ink wastewater to below its predetermined standard adopted from WHO and Environmental Quality Regulation 2009. For this purpose, the wastewater was investigated by analyzing its characteristic including pH, TSS, TDS, BOD, colour, turbidity and COD. Meanwhile, activated carbon used is PKSAC (Palm Kernel Shell Activated Carbon). COD adsorption studies with this activated carbon were carried out under different conditions and influence by different parameters such as pH and bed height in column adsorption. The performance study showed the condition in which pH does not show significant effect on the COD removal and the highest percentage of COD removal were found at bed height 3 cm with the percentage removal of 65%. This indicate, % of COD removal increase with increasing in bed height. Furthermore, the minimum bed height required to treat the water sample was recorded to be 0.8 cm analyzed by BDST model. The present study prove that the activated carbon was one of the effective ways in removal of COD.

Treatment of printing ink wastewater using electrocoagulation

The present study investigates the treatment of real printing ink wastewater by using the electrocoagulation (EC) process. Effects of initial chemical oxygen demand (COD) concentrations, electrode materials and current densities were examined to determine the maximum COD and color removal from the wastewater. In parallel, raw and treated printing ink wastewater toxic potential was further estimated via the application of toxicity tests using the freshwater crustacean Thamnocephalus platyurus for assessing EC process efficiency. According to the results, it was observed that the EC is efficient under most of the operating conditions used, as COD and color removal ranged between 72.03 to 85.81% and 98.7–100%, respectively. The total cost of the EC process, considering the treatment time, applied current, applied voltage and the total anode electrode mass consumption was also estimated. The Fe electrode proved to be of lower cost than the Al electrode, however the use of Al electrode produced better decolorization results in the solutions. Moreover, toxicity tests currently performed with the use of larvae of the fairy shrimp Thamnocephalus platyurus revealed a substantial decrease in the toxic potential of printing ink wastewater, thus indicating the efficiency of the proposed EC process.

APPLICATION OF ELECTRO-COAGULATION FOR TREATMENT OF WASTEWATER FROM PACKAGE PRINTING PROCESS

Printing wastewater is generally considered as hazardous waste whose treatment and disposal are strictly regulated. Although electro-coagulation (EC) process has been successfully applied for the treatment of different types of wastewater, its application for printing wastewater is rarely reported. In this study, EC was applied to treat the printing ink wastewater, taken from a paper packing factory in An Giang Plant Protection Join Stock Company, which was highly colored and contaminated with organic compounds. The treatment process was performed using aluminum electrodes for two hours. Effects of applied voltage (5 - 40 V), pH (5 - 9), electrodes distance (1 - 5 cm), salt concentration in electrolyte solution (0.05 - 0.4 g/L), and the rotational speed of stirring (0 - 400 rpm) on the removal efficiencies of color and COD were investigated. Based on the effects of various factors, optimum condition for the treatment was given. Results showed that the EC process can effectively remove color and COD for 30 min. The effluent quality in terms of color and COD met well National Technical Regulation on Industrial Wastewater (QCVN 40-2011/BTNMT, column B). Finally, a comparison in removal efficiencies between the processes of EC and chemical-coagulation was also presented.

Degradation of Painting Ink Wastewater in a Tubular Reactor with Electrochemical Treatment

In the present study, electrochemical treatment experiments were conducted to degrade water-based printing ink wastewater. It was performed with ruthenium oxide coated titanium acting as anode and stainless steel tube as cathode. Electrolyses carried out in batch under steady conditions and operating at constant flow velocity between 0.538×10-3 and 6.129×10-3m/s. The evolution of color and COD removal, the value of pH were found to be inter-related. The kinetics for the concentration decays of the wastewater pseudo first-order reaction that is characteristic for a mass transfer controlled operation. The mass transfer coefficient kc increased with increasing flow velocity and Reynolds number. The evolution of color and COD removal, the value of pH were found to be inter-related. The effect of the parameters on current efficiency and energy cost has also been investigated. The tubular electrochemical reactor could be considered a feasible and an effective alternative system for the electrochemical treatment of water-based printing ink wastewater.

Treatment of printing wastewater by a combined process of coagulation and biosorption for a possible reuse in agriculture

A coagulation–flocculation process was used to treat water-based printing ink wastewater in optimal conditions. A biological process treatment was combined to coagulation–flocculation process using fungal biomass biosorption capacity. Combined process has a significant effect on color removal and on COD removal (80%). The potential of reusing treated wastewater in agriculture was investigated. Germination tests of five species were carried out using treated and untreated wastewater and show that these effluents could be adequately recycled in culture irrigation.

English

A coagulation–flocculation process was used to treat water-based printing ink wastewater with aluminum sulphate {Al2(SO4)3} as coagulant and with Praestol as flocculant. To minimize turbidity and sludge volume index (SVI), the experiments were carried out using jar tests and response surface methodology (RSM) was applied to optimize this process. A central composite design, which is the standard design of RSM, was used to evaluate the effects and interactions of three factors, that is, coagulant dosage, flocculant dosage and pH on the treatment efficiency. The optimal conditions obtained from the desirable response, chemical oxygen demand (COD) removal, were coagulant dosage of 8250 mgl-1, flocculant dosage of 80 mgl-1 and pH 7.25, respectively. The RSM was demonstrated as an appropriate approach for the optimization of the coagulation–flocculation process by confirmation experiments. Key words: Printing ink industry effluent, chemical oxygen demand (COD) removal, response surface methodology, coagulation-flocculation process.

Treatment of water-based printing ink wastewater by Fenton process combined with coagulation

Attempts were made in this study to examine the efficiency of Fenton process combined with coagulation for treatment of water-based printing ink wastewater. Parameters affecting the Fenton process, such as pH, dosages of Fenton reagents and the settling time, were determined by using jar test experiments. 86.4% of color and 92.4% of chemical oxygen demand (COD) could be removed at pH 4, 50 mg/l H 2O 2, 25 mg/l FeSO 4 and 30 min settling time. The coagulation using polyaluminium chloride (PAC) and ferrous sulfate (FeSO 4) was beneficial to improve the Fenton process treated effluent in reducing the flocs settling time, enhancing color and COD removal. The overall color, COD and suspended solids (SS) removal reached 100%, 93.4% and 87.2% under selected conditions, respectively. Thus this study might offer an effective way for wastewater treatment of water-based ink manufacturer and printing corporation.

The role of zeolites in wastewater treatment of printing inks

The adsorption of residual organic pollutants from flocculated printing ink wastewater onto several synthetic zeolites was investigated as a finishing method for additional reduction of TOC. The nonselective removal of total organic content was studied. The amount of adsorbed organics was largest for ZSM-5 and NH 4-Beta while the other zeolites studied showed lower efficiency, suggesting that adsorption is independent of pore structure. The adsorption rates of organic pollutants were fast. Although the TOC removal increases with increasing amount of zeolite, because of the necessity of additional filtration to lower turbidity to required levels, 5.0 g/L of zeolite was found to be optimum. The 88% reduction of TOC obtained with a single flocculation treatment was improved with the combination of flocculation and adsorption with ZSM-5 which resulted in the overall TOC efficiency of 95%. The addition of zeolites in decantated supernatant water, obtained after flocculation, was also studied in order to assess the effect of floc on zeolite capacity. A decrease in adsorption capacity occurred only if a coagulant concentration less than optimal was applied. Removal efficiency then decreased by around 10%. It was concluded that flocculation followed by adsorption with zeolites is an effective treatment method for this kind of wastewater.

Biological treatment of printing ink wastewater

Printing ink wastewater is usually very difficult to treat biologically and its chemical oxygen demand (COD) far exceeds standards of discharge. The COD in wastewater is usually 3,000 to 8,000 mg/L after flocculation and sedimentation. Herein, a strain of bacterium was isolated from the sludge and identified as Bacillus sp. and utilized to treat printing ink wastewater. The application of bacteria to degrade printing ink in wastewater is discussed in this paper. The influence of N and P sources on COD removal, and COD removal in combination with glucose was also discussed. More than 85 per cent of the COD could be removed using the proposed biological process. A novel internal airlift loop bioreactor with bacteria immobilized onto ceramic honeycomb support was used for the wastewater treatment.

Pre-Treatment of Currency Printing Ink Wastewater through Coagulation-Flocculation Process

Attempt has been made to study the treatability of printing ink wastewatergenerated from an Indian currency printing press using coagulation-flocculation process. Coagulant agents, viz. ferrous sulphate, ferric chloride, aluminium sulphate and polyaluminium chloride were studied to select the most suitablecoagulant for effective treatment, and attain the optimum coagulant concentration. Cationic polyeletrolyte in conjunction with the most effective coagulant was also studied to assess its effect on floc settleability. Polyaluminium chloride (PAC) was found to be the most efficient coagulant, achieving removals of colour, suspended solids (SS), biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of 95.9–96.5%, 96.5–97.0%, 61.3–65.8%and 54.8–61.8%, respectively at an optimum concentration of 1500 mg L-1. Other coagulants, viz. ferrous sulphate, ferric chloride and aluminium sulphate did not show substantial removals of colour, BOD and COD, except suspended solids in comparison to the performance of PAC. Cationic ploylectrolyte in combination with PAC at an optimum concentration of 1500 mg L-1 of PAC and 1.0 mg L-1 of polyelectrolyte further improved the removal efficiency of various parameters studied, in addition to improving the floc settling rate, and reduction in quantity of sludge generation.Effect of rapid mixing intensity expressed as mean temporal velocity gradient (G), and mixing time (t) on flocculation was also investigated. Rapid mixing at an impeller rotational speed (n) of 300 rpm and mixing time (t) of 60 sec indicated good floc formation, which resulted in achieving velocity gradient of 821 s-1, and was found to be an optimum combination. This was also indicated by relatively high settling velocity of sludge formed and low residual colour in the supernatant. However, slow mixing beyond 5 min, adopted after initial optimum rapid mixing, indicated negligible effect on flocculation.

Optimization of Coagulants for Pretreatment of Printing Ink Wastewater

This study was aimed at the optimization of a coagulant agent for the treatment of printing ink wastewater generated from a currency printing press through flocculation studies. Coagulant agents, viz. ferric chloride and polyaluminum chloride, were evaluated to select the most suitable coagulant for effective treatment, and attain the optimum coagulant concentration in comparison to calcium chloride being presently used. Cationic polyelectrolyte, in conjunction with the most effective coagulant, was also studied to assess its effect on floc settleability. Polyaluminum chloride (PAC) was found to be the most efficient coagulant, achieving color, suspended solids (SS), biochemical oxygen demand (BOD), and chemical oxygen demand (COD) removals of 96, 97, 63, and 58%, respectively, at an optimum concentration of 1500 mg/L. Ferric chloride did not show substantial removals of color, BOD, and COD, except suspended solids in comparison to the performance of PAC. Cationic polyelectrolyte, in combination with PAC at an optimum concentration of 1,500 mg/L of PAC and 1.0 mg/L polyelectrolyte, further improved the removal efficiency of various parameters studied, in addition to improving the floc settling rate, and reduction in quantity of sludge generated. In comparison to calcium chloride presently in use at the currency printing press under study, performance efficiency of PAC in conjunction with cationic polyelectrolyte proved to be more effective. In addition, reduction in volume of sludge generation was 62.5% by using PAC and polyelectrolyte compared to calcium chloride. Cost analysis revealed that use of PAC and polyelectrolyte at optimum concentrations would result in a savings of around 56% in recurring cost of coagulant for a flow of 75 m3 per day.

Flocculation as a Treatment Method for Printing Ink Wastewater

To find a suitable method for treating printing ink wastewater, the fundamental behavior and characteristics of two kinds of experimental flexographic printing ink wastewater were studied. The differences between the two prepared wastewaters were the use of different kinds of binders–resins and pigments and different solvent contents representative of real printing inks. Examination of the water quality characteristics of the simulated wastewaters confirmed that the wastewaters were too highly loaded with organic substances for discharge and were not biodegradable. The prepared wastewaters also showed some colloidal dispersion properties. Such properties were strongly affected by pH. As pH decreased, the negative electrical charge of the particles was neutralized, resulting in their aggregation. Therefore, the present study focused on optimizing flocculation processes to destabilize the dispersions. Inorganic electrolytes were found to be more efficient flocculants than the organic polyelectrolytes tested. Even when added in very small quantity, inorganic electrolytes caused extensive neutralization of particle charges and consequent floc formation. The optimum flocculant concentration was determined on the basis of electrokinetic (zeta) potential and turbidity measurements. Mixing intensity, expressed as the mean mixing velocity gradient (G), and time of mixing (t) were investigated, and the optimum Gt product (GtOPT 4.45 × 104) was determined using turbidity values of supernatant water and sedimentation velocity of obtained flocs as criteria for flocculation efficiency. Flocculation was shown to be a simple and efficient treatment from an economic and technical point of view. It was capable of removing a substantial portion of the organic content, completely removing color and turbidity.